In optical communication systems, messages are transmitted by electromagnetic carrier waves at optical frequencies that are generated by sources such as lasers and light-emitting diodes. One preferred device for routing or guiding waves of optical frequencies from one point to another is an optical waveguide. The operation of an optical waveguide is based on the fact that when a light-transmissive medium is surrounded or otherwise bounded by an outer medium having a lower refractive index, light introduced along the axis of the inner medium substantially parallel to the boundary with the outer medium is highly reflected at the boundary, trapping the light in the light transmissive medium and thus producing a guiding effect between channels. A wide variety of optical devices can be made which incorporate such light guiding structures as the light transmissive elements. Examples, without limitation, include planar optical slab waveguides, channel optical waveguides, rib waveguides, optical couplers, optical splitters, optical switches, optical filters, arrayed waveguide gratings, waveguide Bragg gratings, variable attenuators and the like. For light of a particular frequency, optical waveguides may support a single optical mode or multiple modes, depending on the dimensions of the inner light guiding region and the difference in refractive index between the inner medium and the surrounding outer medium.
Organic polymeric materials can be used to construct optical waveguide and interconnect devices such as those given above. However, whereas single mode optical devices built from planar waveguides made from glass are relatively unaffected by temperature, devices made from organic polymers may show a significant variation of properties with temperature. This is due to the fact that organic polymeric materials have a relatively high thermo-optic coefficient (dn/dT). Consequently, a change in temperature causes the refractive index of an optical device made from a polymeric material to change appreciably. This ability to have a change in polymer refractive index due to a temperature change can be used to make active, thermally tunable or controllable devices incorporating light transmissive elements. One example of a thermally tunable device is a 1×2 switching element activated by the thermo-optic effect. In such a device light from an input waveguide may be switched between two output waveguides by the application of a thermal gradient induced by a resistive heater for which the heating/cooling processes occur over the span of one to several milliseconds.
A critical requirement for telecommunication devices is to achieve low insertion loss; which means that the materials used in waveguides and optical devices should have low levels of light absorption. While special, high purity glass has been used in many glass telecommunications applications, in recent years there has been considerable research into polymeric materials which can be used by the telecommunications industry instead of glass. Polymers have several advantages over glass materials. For example, they can be easily formulated to specifically match desired properties or can be reacted with other polymeric material to achieve the desired characteristics; and they can be worked at lower temperatures than glass. However, traditional carbon-hydrogen polymeric materials also have certain undesirable characteristics. In particular, when polymeric materials are used in telecommunications devices, the absorption in the near IR for organic materials is linked to the presence of E—H covalent bonds (E=N, O or C) that have stretching vibration bands at energies between 2800 and 3500 nm. Overtones and combinations bands involving these E—H bonds can increase significantly the absorption loss at 1550 nm. In addition, O—H and N—H bonds, which may be present in polyimides and polyacrylates for exemple, contribute very strongly to absorption at wavelengths near 1310 nm as well as at 1550 nm. Thus, the presence of O—H and N—H bonds is particularly detrimental to low losses. Thus, the presence of O—H and N—H bonds is particularly detrimental to low losses. Consequently, for telecommunications uses it would be desirable to produce polymerizable organic materials that have no or very few C—H, O—H and N—H bonds. Comparatively speaking, it is relatively easy to prepare polymerizable materials that do not contain O—H and N—H bonds. The removal of all C—H bonds from a molecular structure is a much more difficult task to accomplish.
Considerable research has been done concerning the replacement of C—H bonds by C—F bonds. However, very few organic materials are totally fluorinated, TEFLON being the best known example. In addition, even where monomeric C—H materials can be fully fluorinated, such perfluorinated monomers do not polymerize easily. Moreover, it is very difficult to process such the perfluoro polymers into telecommunications devices such as waveguides and planar devices.
While considerable efforts have been devoted to seeking polymerizable compounds having fluorinated alkyl attached to a polymerizable moiety, for example, an acrylate group, much less effort has been devoted to seeking novel polymerizable species in which the polymerizable group is directly attached to a fluorinated aromatic ring. Examples of compounds having fluorinated aromatic rings can be found in the following U.S. Pat. No. (title): 3,637,866 to Pasquale et al (Substituted Perfluoro Diphenyl Ethers); U.S. Pat. No. 3,661,967 to Anderson et al (Cyano Containing Polyfluoroaromatic Compounds); U.S. Pat. No. 4,420,225 to Bömer et at (Lens Of A Homo- Or Copolymer Of A Fluorine Containing Styrene Polymer); and U.S. Pat. No. 6,333,436 B1 (Styrene Derivatives). In particular, there are not many known compounds in which a fluorinated aromatic ring, and particularly highly fluorinated aromatic rings are directly attached to vinylic groups (—CH═CH2).
Consequently, even though considerable research has been directed to the development of fluorine containing polymerizable materials, the need exists for addition materials in this area. In particular, there continues a need for fluorine containing polymerizable material that have low absorption losses in the 1550 nm and 1300 nm region in which telecommunications devices operate.